Apparatus and method for detecting bacterial growth beneath a wound dressing

ABSTRACT

An apparatus and method are provided for visually monitoring, detecting, and/or determining the presence, absence, and/or growth of harmful or potentially harmful bacterial microorganisms beneath a wound dressing, in one example used to cover an indwelling central venous catheter or other catheter. A bacteria detection apparatus includes a barrier membrane, a permeable membrane for placement proximate a wound or a catheter insertion site, and an indicator between the barrier membrane and the permeable membrane for indicating the presence of bacteria proximate the permeable membrane. A method of using a bacterial growth detection apparatus is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Pat. No.8,153,394, issued on Apr. 10, 2012, which is a divisional application ofU.S. Pat. No. 7,749,531, issued Jul. 6, 2010, each of which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates generally to medical indicator devicesand, more particularly, to an apparatus and method for detectingbacterial microorganisms related to a wound dressing or a dressing usedto cover an indwelling catheter.

BACKGROUND

Central venous catheters and other catheters inserted through the skinand into the lumen of an artery or vein are widely used in a variety ofpatients usually in the hospital setting. They provide secure andimmediate venous access and allow for the safe administration of fluidsand drugs. However, catheter related bloodstream infection (CR-BSI) is aserious and potentially life-threatening complication when catheters andinsertion sites become infected with bacterial microorganisms. Theinsertion sites for these catheters are routinely covered with adressing as a preventive measure for bacterial infections.

Intravascular catheters are employed routinely in healthcare settingsfor a number of purposes including infusion of pharmacological drugs andfluids, hemodialysis, monitoring of pressures, and sampling of blood.Although these catheter devices are essential components of modern daymedical care, they are also susceptible to microbial contamination.Microbial pathogens can attach to the catheter surface at the site ofpenetration into the skin. A number of factors renders catheter implantsespecially susceptible to microbial contamination. Firstly, the catheteressentially compromises the skin's natural protective barrier, providinga direct route to bypass the body's first line of immunity. In addition,upon insertion into the host, the outer surface of the catheter isquickly covered with host proteins that facilitate microbial attachment.There is also evidence that implanted abiotic material itself causeslocal attenuation of antimicrobial immune responses, thereby providing afertile breeding ground for microbial biofilm formation. Finally,patients who possess the greatest need for catheterization are oftenimmunologically compromised and are therefore more susceptible tobacterial infection.

Catheters themselves are generally infected via one of two generalroutes, typically by organisms that compromise the natural florasurrounding the site of catheter insertion. First, microbes maycontaminate the catheter along its outer surface, and it is believedthat this type of infection often occurs during the initial insertion ofthe catheter through the skin. Catheters can also be contaminated intheir lumenal compartments where fluids flow from contaminated infusatesolutions. The most prevalent bacteria found to be the cause ofbacterial sepsis from the exterior flora surrounding the insertion siteinclude, but are not limited to, coagulase negative Staphylocci,Staphylococcus epidermitus, Staphylococcus aureus, Escherichia coli,Enterobacter cloacae and Pseudomonas aeruginosa.

Catheter-related bloodstream infections are notoriously difficult totreat via conventional antibiotic therapy, with associated mortalityrates ranging from 12% to 25%. Catheter related bloodstream infection isthe most frequent serious complication seen with catheters withinfections occurring in as many as 3% to 7% of all catheter placements,which is estimated to be more than 250,000 patients in U.S. hospitalseach year. In addition, these infection complications extend hospitalstays, necessitate active intervention on the part of healthcarepersonnel, and result in driving the estimated annual domestichealthcare cost associated with complications arising from thesecatheter-related infections to more than nine billion dollars.

The presence and growth of harmful and/or potentially harmful bacteriabeneath wound dressings or dressings used to cover, indwelling centralvenous catheters has been shown to cause serious infection, illness, andeven death if the bacterial growth goes unnoticed and untreated for evena relatively short period of time. The most prevalent pathogenicbacteria found to be the source of septic infections include, but arenot limited to, coagulase negative staphylocci, Staphylococcusepidermitus, Staphalocaccus aureus, Escherichia coli, Enterobactercloacae, and Pseudommonas aeruginosa. These bacteria can enter the bloodstream causing serious and life-threatening illness.

Recent advances in catheter compositions have shown to be relativelysuccessful in preventing some bacterial growth. Some catheters have beencoated with antibacterial growth materials, chemicals, and drugs in aneffort to prevent infections from entering the bloodstream by way ofthis conduit. Wound dressings used to cover these catheter insertionsites have similarly been treated with antibacterial agents to inhibitbacterial growth. In most cases the effort has been focused on materialsand pharmaceuticals used to prevent bacterial growth. Dressings used tocover indwelling catheters in the hospital setting are also routinelychanged and the puncture site carefully examined for bacterialinfection. However, an apparatus and method for early warning orindication of the presence of harmful bacterial growth has not beenavailable for use with catheters.

Thus, an apparatus and method for detecting and easily indicatingbacterial growth is not presently known but highly desirable.

SUMMARY

The present invention provides an apparatus and method for visuallydetecting bacterial growth related to wound dressings or catheterinsertion sites at an early stage of growth for advantageously remedyingthe bacterial growth.

In accordance with an embodiment of the present invention, a bacterialgrowth detection apparatus is provided, the apparatus including abarrier membrane, a permeable membrane for placement proximate a wound,and an indicator between the barrier membrane and the permeable membranefor indicating the presence of bacterial growth proximate the permeablemembrane.

In accordance with another embodiment of the present invention, anotherbacterial growth detection apparatus is provided, the apparatusincluding a barrier membrane including a transparent hydrophobicpolymeric membrane, and a permeable membrane including a transparenthydrophilic polymeric membrane, the permeable membrane for placementproximate a wound or catheter insertion site. The detection apparatusfurther includes an indicator between the barrier membrane and thepermeable membrane, the indicator capable of detecting a pH changecaused by byproducts of bacterial growth diffused through the permeablemembrane.

In accordance with yet another embodiment of the present invention, amethod of detecting bacterial growth is disclosed, the method includingproviding a bacterial growth detection apparatus as described above,placing the permeable membrane over a wound or catheter insertion site,detecting a pH change caused by byproducts of bacterial growth, andindicating the presence of the byproducts of bacterial growth with avisible change of the indicator.

The scope of the invention is defined by the claims, which areincorporated into this section by reference. A more completeunderstanding of embodiments of the present invention will be affordedto those skilled in the art, as well as a realization of additionaladvantages thereof, by a consideration of the following detaileddescription of one or more embodiments. Reference will be made to theappended sheets of drawings that will first be described briefly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top view of a bacterial growth detection apparatus inaccordance with an embodiment of the present invention.

FIG. 2 shows an exploded side view of the bacterial growth detectionapparatus of FIG. 1 in accordance with an embodiment of the presentinvention.

FIG. 3 shows an assembly view of the bacterial growth detectionapparatus of FIG. 1 in accordance with an embodiment of the presentinvention.

Embodiments of the present invention and their advantages are bestunderstood by referring to the detailed description that follows. Itshould be appreciated that like reference numerals are used to identifylike elements illustrated in one or more of the figures. It should alsobe appreciated that the figures may not be necessarily drawn to scale.

DETAILED DESCRIPTION

The present invention provides an apparatus and method for visuallymonitoring, detecting, and/or determining the presence, absence, and/orgrowth of harmful or potentially harmful bacterial microorganismsbeneath a wound dressing or a catheter insertion site, in one exampleused to cover an indwelling central venous catheter or other catheterused for insertion into the lumen of an artery or vein or other skinpuncture site in which a wound dressing or a catheter insertion sitecovering may be prescribed and applied.

Various bacterial microorganisms may be detected with the presentinvention, including but not limited to Staphalocaccus aureus,Staphylococcus epidermitus, Streptococcus mitis, Streptococcus sanguis,Enterococcus faecium, Escherichia coli, Enterobacter cloacae,Enterobacter aerogenes, Enterococcus faecalis, Pseudomonas aeruginosa,Klebsiella pneumonia, Candida albicans, and gram negative bacilli.

In one embodiment of the present invention, a semipermeable/permeablehydrophilic/hydrophobic polymeric composition of membranes with anindicator layer is incorporated with a wound dressing material for thedetection of harmful or potentially harmful bacterial microorganisms.The wound dressing or catheter insertion site material may also beprovided with certain coverings which allow for the easy application ofthe wound dressing to the skin at the site of catheter insertion.Various catheters may be used, including but not limited to those usedfor central venous access placed in the arm or leg or those used formonitoring, such as the Swan-Ganz catheter used for measuring cardiacoutput and often placed in the jugular vein. Sterilization of thedetection apparatus elements, including a barrier membrane, a permeablemembrane, and an adhesive, may be provided using conventional means suchas radiation sterilization or gas sterilization procedures. Conventionalpeel-pack may also be used for each detection apparatus.

Advantageously, the present invention provides an early warning of thepresence/growth of harmful or potentially harmful bacterialmicroorganisms beneath a wound dressing or dressing used to cover anindwelling catheter (e.g., in a hospital setting) such that earlydetection may prompt intervention to mitigate the microbial growth at anearly stage of potential infection.

Referring now to FIGS. 1, 2, and 3, a top view, an exploded side view,and an assembly view, respectively, of a bacterial growth detectionapparatus 100 are shown in accordance with embodiments of the presentinvention. Detection apparatus 100 includes an indicator 120 between abarrier membrane 114 and a permeable membrane 118. An adhesive 116 isprovided around the circumference of barrier membrane 114. Optionally,the present invention may be packaged between sheet liners 102 and 110.

In one example, barrier membrane 114 is a transparent, hydrophobic, andpolymeric barrier membrane that acts as a barrier to the outsideenvironment. Water, water vapor, and/or bacterial growth are preventedfrom penetrating to the wound or catheter insertion site from theenvironment by barrier membrane 114. Barrier membrane 114 does permitthe passive diffusion of water vapor and oxygen from under the wounddressing or catheter insertion site to the environment. Barrier membrane114 further permits the passive diffusion of oxygen from the environmentthrough the barrier membrane to the skin and creates a moist environmentat the surface of the skin and wound or catheter insertion site whilelimiting water vapor loss from the underlying tissue.

The term “barrier composition” or “barrier membrane” is used throughoutthe specification to describe a transparent hydrophobic polymericmembrane which is used as the outermost component of the wound dressingor catheter insertion site when applied to the skin and is used toprevent water or water vapor or bacteria from penetrating through theouter layer from the environment and to the wound or catheter insertionsite. This polymeric barrier permits the passive diffusion of watervapor and oxygen from under the wound dressing to the environment. Itfurther permits the passive diffusion of oxygen from the environmentthrough the barrier membrane to the skin and creates a moist environmentat the surface of the skin and wound or catheter insertion site whilelimiting water vapor loss from the underlying tissue.

Barrier compositions or membranes/films which may be used in accordancewith the present invention include but are not limited to poly(vinylidene fluoride), poly (vinylidene chloride), phenoxy resins,butadiene/styrene copolymers, butadiene/methylstyrene copolymers,poly(meth)acrylates, butadiene/acrylonitrile copolymers,ethylene/propylene copolymers, polybutadiene, polyisoprene,poly(oxy-2,6-dimethyl-1,4-phenylene),poly(oxycarbonyloxy-1,4[1,4-phenyleneisopropylidene-1,4-phenylene),acrylonitrile styrene copolymers, acrylonitrile/methylacrylate/butadiene copolymers, acrylonitrile/styrene/butadienecopolymers, poly-1-vinylaphthalene, polyvinylphenyl ketone,poly-p-xylylenedodecanedioate, poly-tetramethylene octenediamide,poly-tetramethylene terephthalene, poly-trimethylene-3,3′-dibenzoate,poly-terephthallic anhydride, poly-4-methyl-diamine, polyvinylenecarbonate, polyvinylene laurate, polyisoprpenyl acetate,polyallylbenzene, polyvinylbutyl ether, polyvinyl formate, polyvinylphenyl ether, polynorbornadine, polycarbonate, hydrophobic polyestersand polyurethanes, and mixtures thereof.

Barrier membrane 114 includes an adhesive 116 that is used to contactthe skin and make a secure bond that is a perimeter of adhesionsubstantially along the border of barrier membrane 114. Adhesive 116 isa medical grade adhesive along the circumference/border of barriermembrane 114 and prevents apparatus 100 from being dislodged orinadvertently removed from the skin.

Permeable membrane 118 is beneath (i.e., closer to the wound or catheterinsertion site or skin) barrier membrane 114 and, in one example, is asecond transparent, permeable or semipermeable, hydrophilic, andpolymeric membrane. Permeable membrane 118 does not extend fully to themargins of barrier membrane 114 but is held in place by adhesive 116used to secure the wound dressing and indicator to the skin. Permeablemembrane 118 is permeable to gases, water vapor, and gases dissolved inwater vapor in one example. In yet another example, permeable membrane118 is permeable to gases that include, oxygen, carbon dioxide, carbonmonoxide, hydrogen sulfide, hydrogen, sulfur dioxide and ammonia amongothers, such that the concentration of gas which may ultimately diffusethrough the polymeric composition is sufficient to produce a visualcolorimetric reaction with indicator 120 which is contained or“sandwiched” between the inner permeable membrane 118 and the outerbarrier membrane 114.

The term “hydrophilic semipermeable polymeric composition” or “permeablemembrane” is used to describe the chemical composition of thetransparent membrane that is in closer proximity to the skin and thewound or catheter insertion site than the barrier membrane. Thepermeable membrane may be in contact with the skin at most of itssurface that is proximal to the skin. This membrane is permeable togases, water vapor and gases dissolved in water vapor. It is permeableto gases including but not limited to oxygen, carbon dioxide, carbonmonoxide, hydrogen sulfide, hydrogen, sulfur dioxide, and ammonia amongothers, such that the concentration of gas which may ultimately diffusethrough the polymeric composition is sufficient to produce a visualcolorimetric reaction with the indicator which is between the innersemi-permeable membrane and the outer barrier membrane.

A number of hydrophilic, permeable polymers may be used in the presentinvention, including but not limited to (poly) hydroxyethylmethacrylate, (poly) hydroxypropyl methacrylate, (poly) glycerolmethacrylate, copolymers of hydroxyethyl methacrylate, hydroxypropylmethcrylate or glycerol methacrylate and methacrylic acid, aminoacrylateand aminomethacrylate, (poly) vinylpyridine, polar polyamides, methylcellulose, hydroxypropyl cellulose, hydroxyethyl cellulose,hydroxypropyl methylcellulose, ethylhydroxyethylcellulose, carboxymethylcellulose, cellulose acetate, cellulose acetate butyrate, celluloseacetate propionate, cellulose nitrate, polyvinyl acetate, polyvinylalcohol, copolymers of polyvinylacetate and polyvinyl alcohol, hydroxylmodified copolymers of vinyl acetate and vinylchloride, polyesters andpolyurethanes containing at least 10% by weight of polyethylene oxide,styrene/methacrylic acid/hydroxyethyl methacrylate copolymers,styrene/methacrylic acid/hydroxypropyl methacrylate copolymers,methylmethacrylate/methacrylic acid copolymers, ethylmethacrylate/styrene/methacrylic acid copolymers, ethylmethacrylate/methyl methacrylate/styrene/methacrylic acid copolymers,polytetrafluoroethylene, hydrophilic cellulose copolymers, and mixturesthereof.

Indicator 120 provides a colorimetric reaction upon exposure to thegases produced by the growth of bacterial microorganisms. Gases, whichare produced by the growth of microorganisms, include but are notlimited to carbon dioxide, ammonium, hydrogen sulfide, sulfur dioxide,and hydrogen. Lactate may also be produced as a result of metabolicgrowth to subsequently form lactic acid. In a moist environment, as isthe state beneath the wound dressing or catheter insertion site, thesegases will form an acid (e.g., carbonic, sulfuric acid) or a base (e.g.,ammonia) which reacts with the selected indicator to produce acolorimetric reaction that is easily visualized through barrier membrane114, thereby alerting a user, such as an attending healthcareprofessional, of potentially harmful bacterial growth at the catheterinsertion site.

The term “indicator” is used to describe chemical compounds which may beadded to or coated onto polymeric compositions according to the presentinvention in amounts effective to detect gases which are produced asbyproducts from the growth of microorganisms such as bacterial growththat may be beneath the wound dressing and within the puncture site ofthe skin from a central venous catheter insertion. Indictors arechemical compounds that undergo a chemical reaction in the presence of agas or an acid or base conjugate of a gas and produce a colorimetricspecies in response to the acid or base produced. The chemical responseof the indicator is generally concentration dependent. Indicators foruse in the present invention may be solids or liquids. In the presentinvention, gases which are produced as normal byproducts of bacteria ormicroorganism growth (e.g., carbon dioxide, sulfur dioxide, lactate, andhydrogen) react with the chosen indicator which has been polymerized ordispersed throughout the polymeric composition. The indicator produces acolorimetric reaction upon exposure to the gas or an acid or baseconjugate of the gas, thus indicating the presence of bacterial growthbeneath the wound dressing or catheter insertion site and in closeassociation with the indwelling central venous or other catheter.

Examples of indicators that may be used in the present invention includebut are not limited to phenol red, xylenol blue, bromocresol purple,bromocresol green, Congo red, cresol red, phenolphthalien, bromothymolblue, p-naphtholbenzein, neutral red, a mixture of potassium iodide,mercuric (III) iodide, sodium borate, sodium hydroxide and water nileblue, thymolphthalein, crysol violet, hydroxy naphthol blue, malachitegreen oxalate, methyl orange, alizarin, crystal violet, methyl red, andmixtures thereof.

The compositions for use in the present invention include polymers,which are comprised of substantial quantities of monomers having polargroups associated with them, such that overall polymeric composition isrendered hydrophilic. Preferably, the polymeric compositions arecomprised of monomers which contain for example, hydroxyl groups, estergroups, amide groups, urethane groups, or carboxylate groups. While notbeing limited by way of theory, it is believed that the inclusion ofpolar groups allows water to more readily permeate the polymer andconsequently, bring dissolved gases into proximity of the indicatorcontained within the two membranes and evoke a reaction.

Membranes 114 and 118 may be chemically/physically functionalized (e.g.,to include different functional exchange groups with different backbone)to allow for selective control over passage through the membrane (e.g.,to allow specific molecules to pass and/or for molecules to pass in aspecific direction (e.g., away from or toward the wound site)).

The two polymer membranes 114 and 118 “sandwich” indictor 120 fordetecting the byproducts of bacterial growth such as gaseous carbondioxide, lactic acid, ammonium, hydrogen sulfide, sulfur dioxide, andhydrogen in a dissolved aqueous or vapor state, thereby evoking a changein the color of the indicator if the pH of the immediate environmentbeneath the wound dressing or catheter insertion site changes, therebysignaling the presence/growth of harmful or potentially harmfulbacterial microorganisms. Thus, in one example, a gas released bybacterial microorganisms selected from the group consisting of carbondioxide, hydrogen sulfide, sulfur dioxide, ammonia, lactate, andmixtures thereof, may dissolve in water or water vapor that haspermeated through the permeable membrane, to form one of carbonic acid,sulfuric acid, ammonium hydroxide, lactic acid, and mixtures thereof,thereby causing a pH change and interacting with the indicator to causea colorimetric change.

Advantageously, the present invention provides an “early warning” of thegrowth of infectious microbial pathogens beneath the wound dressing atthe site of catheter insertion. The indicator(s) employed in theinvention reacts to a change in the pH resulting from the byproducts ofmicrobial growth beneath the wound dressing or catheter insertion siteand causes a distinct colorimetric change that can be easily visualizedthrough transparent barrier membrane 114.

The present invention may be packaged in various ways and in oneembodiment is packaged similarly to a dressing apparatus trademarked asTegaderm®, available from 3M Health Care Ltd., of St. Paul, Minn.Optionally, barrier membrane 114, indicator 120, and permeable membrane118 may be packaged between sheet liners 102 and 110 to facilitateapplication of the wound dressing and indicator to the surface of theskin over the site of the indwelling central venous or other catheter.

In one example, sheet liner 102 is a thin and rigid sheet of thin cardon the barrier side or top side of barrier membrane 114, with “wings”104 at each end. Sheet liner 102 may include a window 106 pre-cut suchthat window 106 may be peeled away to reveal barrier membrane 114underneath, thus leaving barrier membrane 114, indicator 120, andpermeable membrane 118 suspended on a frame of sheet liner 102, whichfacilitates precise placement of the film and reduces wrinkling.Accordingly, window 106 may be peeled away and removed just prior toapplication of apparatus 100 to the skin and allows for visualization ofthe catheter insertion site through the two transparent membranes 114and 118 and indicator 120. Sheet liner 102 may also include a slit 108along one side of the border of sheet liner 102 to allow for the peelingaway of the border after the wound dressing is firmly applied to theskin at the site of the catheter insertion.

In a further example, sheet liner 110 is printed sheet of release papercoupled to the adhesive 116 adjacent to permeable membrane 118. Sheetliner 110 may also have wings 112 to aid in application to the skin.Sheet liner 110 is removed just after window 106 of sheet liner 102 isremoved, and the wound dressing applied to the skin over the cathetersite.

It will be apparent that the elements of detection apparatus 100 thatcontact the skin, including but not limited to the barrier membrane, theadhesive, and the permeable membrane, are composed of medical gradematerials and in one example meet the requirements for long-term skincontact as established by the United States Food and DrugAdministration.

By empirical data, growth of certain bacteria under controlledconditions may be correlated to pH such that the bacteria detectionapparatus of the present invention may be calibrated for differentsensitivities (e.g., to show a colorimetric change at an earlier time)or for different types of bacteria.

Embodiments described above illustrate but do not limit the invention.It should also be understood that numerous modifications and variationsare possible in accordance with the principles of the present invention.For example, the elements of a bacterial growth detection apparatus,such as the membranes, indicator, and window, may have various sizes andshapes. Accordingly, the scope of the invention is defined only by thefollowing claims.

I claim:
 1. A method of indicating bacterial growth at a wound site,said method comprising the steps of: I) providing a wound dressingbacterial growth detection apparatus which comprises (a) an indwellingcatheter, and (b) a wound dressing covering the outer portion of thecatheter, the wound dressing comprising: (i) a barrier membrane whichcomprises a transparent hydrophobic polymeric material, (ii) a permeablemembrane which comprises a transparent hydrophilic polymeric membranefor placement proximate a wound, and (iii) an indicator which is capableof signaling bacterial growth at the wound site; II) placing thecatheter at the wound site and placing the permeable membrane of thewound dressing at the wound site on top of the catheter; and III)detecting the presence of bacterial growth by detecting a change in theindicator, wherein the change in the indicator is caused by byproductsof bacterial growth.
 2. The method of claim 1, wherein the byproducts ofbacterial growth are selected from the group consisting of gaseouscarbon dioxide, hydrogen sulfide, sulfur dioxide, hydrogen, ammonium,lactate, and mixtures thereof.